1. Field of the Invention
The present invention relates to a method of transferring data over a computer network that includes the Internet.
2. Description of the Related Art
FIG. 17 relates to a conventional data transfer method xe2x80x9cProxy Serverxe2x80x9d disclosed in, e.g., Nikkei Internet Technology (pp. 130 to 137, March, 1998). Reference numeral 1 designates the Internet; 2 designates an access network including a telephone network or an ISDN; and 3 designates a terminal primarily including a personal computer. Reference numeral 4 designates an access point for connecting the Internet 1 to the access network 2 (e.g., an Internet Service Provider).
Reference numeral 5 designates a data delivery server which provides data pertaining to home pages linked to the Internet 1, shareware programs, freeware programs, and audiovisual information, etc.
Reference numeral 6 designates a proxy server which controls access to the data delivery server 5 on the part of the terminal 3. Reference numeral 10 designates an access request for accessing data stored in the data delivery server 5.
Reference numeral 11 designates a first data transfer for transferring data to the terminal 3 from the proxy server 6.
Reference numeral 12 designates a second data transfer for transferring data to the proxy server 6 from the data delivery server 5.
The operation of the conventional data transfer method will now be described by reference to FIG. 17. When accessing desired data stored in the data delivery service 5, the terminal 3 issues the access request 10 to the proxy server 6 located at the access point 4 of the ISP. Upon receipt of the access request 10, the proxy server 6 checks whether or not the desired data are cached therein. If the data are cached, the data are transferred to the terminal 3 from the proxy server 6 by means of the first data transfer 11, whereby the terminal 3 can receive the desired data. If the data are not cached, the proxy server 6 accesses the data delivery server 5 to thereby fetch the data by means of the second data transfer, simultaneously with transfer of the data to the terminal 3 by means of the first data transfer 11, with the result that the terminal 3 acquires the desired data.
As shown in FIG. 17, according to the conventional data transfer method, in a case where desired data are not cached in the proxy server 6, the proxy server 6 accesses the data delivery server 5 which holds the desired data and caches the data therein simultaneously with transmission of the data to the terminal 3. The Internet 1 has an average data transfer capability of 40 kbps or thereabouts, and data are understood to center on the Internet 1 at all times. In a case where an ISDNxe2x80x94use of which has recently undergone explosive growthxe2x80x94is used as one example of the access network 2, the transfer capability of the access network 2 assumes a value of 64 or 128 kbps, and this capability is ensured for the terminal 3 at all times.
From this fact, in a case where data are delivered directly from the data delivery server 5 connected to the Internet 1 by way of the access network 2 including the ISDN, the data are in effect transferred at an average transfer rate of 40 kbps, because the average transfer capability of the Internet 1 assumes a value of 40 kbps in spite of the fact that the access network 2 has a transfer capability of 64 or 128 kbps. Thus, the data transfer method fails to fully utilize the data transfer capability of the access network 2. If the utilization of data transfer capability of the access network 2 cannot be maximized, the following specific problems arise.
(1) An excessive amount of time is required for transferring data, and the terminal must be powered during transfer of data. The power dissipated by the terminal is increased by an amount corresponding to the excess data transfer time.
(2) Since the excessive amount of data transfer time is required, the charges for utilizing an access network and the charges for maintaining connection with the Internet are increased by amounts corresponding to the excessive amount of data transfer time.
Accordingly, as shown in FIG. 17, in a case where the terminal 3 accesses the data stored in the data delivery server 5, if the data are not cached in the proxy server 6, there will arise a situation similar to that in which the terminal 3 downloads the data directly from the data delivery server 5 without bypassing the proxy server 6. In such a case, problems (1) and (2) arise.
The greater the amount of data to be transferred, the more noticeable the problems. Data recently delivered over the Internet including freeware programs, shareware programs, and application programs which comprise audiovisual data, assume a volume of several tens of megabytes, which is extremely large. Accordingly, solution of such a problem becomes of ever-increasing importance.
Attempts have been made to offer consumers an access network having a transfer capability on the order of megabytes per second, in forms such as an asymmetric digital subscriber line (ADSL) or a fiber to the home (FTTH). Thus, a difference between the transfer capability of the access network and the mean transfer rate of the Internet tends to increase. Even from this viewpoint, development of a data transfer method for making maximum use of the transfer capability of the access network is important.
The conventional data transfer method enables efficient transfer of data cached in the proxy server to the terminal. However, because of the concentration of data within the Internet, data not cached in the proxy server, particularly data of large volume, cannot be transferred while maximum use is made of the data transfer capability of the access network, thus incurring an increase in the power dissipated by the terminal and an increase in the communications fee.
Further, the same problem arises even at the time of transfer of data in the reverse direction, such as that shown in FIG. 18: namely, at the time of a data transfer 30 in which data are transferred from the terminal 3 to the data delivery server 5.
The present invention has been conceived to solve the above problems, and the object of the present invention is to reduce both the power dissipated by the terminal and a communications fee by transferring data between the terminal connected to an access network and a data delivery server connected to the Internet while making maximum use of the data transfer capability of the access network.
To this end, according to a first aspect of the present invention, there is provided a data transfer method for use with a computer network including a terminal, a data delivery server, and a proxy server, the method comprising the steps that:
the terminal requests the proxy server to download data when the terminal downloads the data from the data delivery server;
the proxy server notifies the terminal that the data can be downloaded when the data are cached in the proxy server;
the proxy server downloads the data and caches the thus-downloaded data therein if the data are not cached in the proxy server; and
the proxy server notifies the terminal that the data can be downloaded when caching of the data is completed. According to a second aspect of the present invention, if the data are not cached in the proxy server, the proxy server predicts a time at which the data will be transferred to and cached in the proxy server and become available for transfer to the terminal, and notifies the terminal of the thus-predicted time beforehand.
According to a third aspect of the present invention, if the data are not cached in the proxy server, the proxy server determines whether or not the data delivery server permits transfer of the data to the proxy server, before the proxy server downloads the data from the data delivery server and caches the thus-downloaded data therein, and only when the data delivery server permits transfer of the data, the data are transferred to the proxy server.
According to a fourth aspect of the present invention, if the data are not cached in the proxy server, the proxy server queries a second proxy server as to whether or not the data are cached; and, if the data are cached in the second proxy server, the proxy server notifies the terminal, without downloading the data from the second proxy server, that the data have been directly downloaded from the second proxy server, when reporting completion of downloading the data to the terminal.
According to a fifth aspect of the present invention, there is provided a data transfer method for use with a computer network including a terminal, a data delivery server, and a proxy server, the method comprising the steps that:
the terminal requests the proxy server to transfer data stored in the terminal to the data delivery service when the data are transferred from the terminal to the data delivery server;
the proxy server downloads the data and caches the thus-downloaded data therein;
the proxy server transfers the thus-cached data to the data delivery server when caching of the data is completed; and
the proxy server notifies the terminal that the data have been transferred to the data delivery server when transfer of the data is completed.